The legal battle over gay marriage in California will continue today when attorneys representing San Francisco, the state, gay couples and groups opposed to same-sex unions argue before a state appeals court.

The San Francisco-based First District Court of Appeal will hear six cases — four in favor of legalizing same-sex unions and two against them — that hinge on whether a trial judge last year correctly ruled that existing marriage laws are unconstitutional.

The case comes nearly two and a half years after marriage licenses were first handed out to gay couples at San Francisco City Hall, in a clear challenge to the state law.

Chief Deputy City Attorney Therese Stewart will be representing San Francisco during the morning arguments, said Matt Dorsey, a spokesman for the City Attorney’s Office.

“This litigation is important. California is the largest state and has the largest gay and lesbian population in the U.S.,” said Jennifer Pizer, an attorney for the Lambda Legal Defense and Education Fund. “Progress is important in a large state with a large community” of gays and lesbians.

Pizer expects gay marriage to become law in California within five years, she said.

The March 2005 ruling by San Francisco Superior Court Judge Richard Kramer found that current marriage laws violate the civil rights of gays and lesbians. Gay marriage opponents hope to overturn Kramer’s ruling.

“Judge Kramer ignored evidence about children being best served by a mother and a father,” said Randy Thomasson, executive director of Campaign for Children and Families, one of the groups that brought the legal challenge. “California since the beginning of the state has honored marriage between a man and a woman … The beauty of marriage is that it produces for children the best chance for stability.”

This week’s legal wrangling comes on the heels of last week’s defeat in New York, where that state’s high court ruled that permitting marriage only between a manand a woman is constitutional.

Additionally, in Georgia, the state Supreme Court last week agreed that a 2004 ballot referendum banning gay marriage was legal.

The state Legislature last year became the first lawmaking body in the country to legalize gay marriage. The governor vetoed the bill, saying it was up to voters or the courts, not lawmakers, to settle the issue.